As semiconductor devices including a transistor or the like come to be manufactured more finely, influence of particles (foreign substances) on yield is being increased. In addition, a need to suppress generation of foreign substances in a film-forming process performed as one process among processes of manufacturing a semiconductor device is also increasing. For example, even when a thin film such as an insulating layer or the like constituting a sidewall spacer (SWS) of a gate electrode included in the transistor is formed, a need to suppress generation of foreign substances in the film-forming process is increased. A silicon carbonitride film (a SiCN film) formed by adding carbon (C) into a silicon nitride film (a SiN film) or a silicon oxycarbonitride (a SiOCN film) formed by further adding oxygen (O) thereto is used as the thin film constituting the sidewall spacer or the like. Since such an insulating layer requires high step coverage characteristics, in many cases, the insulating layer may be formed by a film-forming method such as an alternate supply method of alternately supplying a plurality of kinds of processing gases, or the like.